1. Field of the Invention
This invention relates to a color imaging device, and, more particularly, to a color imaging device having a combination of a solid image pickup element with a color filter.
2. Description of the Prior Art
When, in a solid image pickup element of charge transfer type such as a CCD or the like, an intense light impinges on a part of the element, electric charges generated thereby may flow thereover into adjacent elements to break down the picture image over a wide area on the picture plane, as is known as "blooming".
In order to prevent such blooming, it has been proposed to provide, in a case of a frame transfer type CCD, an anti-blooming gate and an anti-blooming drain to absorb overflown charges.
FIG. 1 shows an image pickup part of a conventional CCD having anti-blooming drains at the boundaries of the picture elements in the horizontal direction and also shows the state of the potential well thereof.
Between the picture elements 1a-1d, anti-blooming gates 2a-2c and anti-blooming drains 3a-3c are formed. In the part (b) in FIG. 1, the shaded portions represent the stored charges. When an intense light impinges on the solid image pickup element and a large number of electric charges are generated thereby, the charges will flow over the anti-blooming gates 2a-2c into the anti-blooming drains 3a-3c. Thus, blur of the picture image due to the blooming is suppressed to minimum.
In the prior art arrangement shown in FIG. 1, however, the area occupied by the anti-blooming parts (gates 2 and drains 3) will increase with the increase of the number of the picture elements in the horizontal direction. Thus, the number of the picture elements is disadvantageously restricted provided that the dimension of the picture plane is fixed. Further, the light incident on the anti-blooming gates and anti-blooming drains does not contribute to effective outputs, and therefore, the utilization efficiency of the light and the sensitivity are degraded.
Improved prior art arrangements which are free from the above disadvantages are shown in FIGS. 2 and 3.
In the FIG. 2 arrangement, which is one such as disclosed in Japanese Patent Application Laid-Open No. 24530/1979, usual channel stoppers 4 and anti-blooming parts 2 and 3 are alternatingly provided at the boundaries between the picture elements. Although the disadvantages involved in the FIG. 1 arrangement are solved herein, other problems are offered. First, since the sampling positions of the picture elements are not equidistant, there may occur moire in the produced luminance signals (i.e. the phenomenon of turn-back of high range components of the picture image to low range). Second, when use is made of an R(red)-G(green)-B(blue) or an R(red)-G(green)-Cy(cyan) stripe type filter which is effective, in combination of the frame transfer type CCD, to perform superior detection of a color picture image, the periodical structure in the horizontal direction is provided by six picture elements. Thus there occurs image distortion of the very low frequency component. Such six-picture-element periodical structure is of so low frequency that there may occur moire even in the case of an object which does not have fine patterns. As the result, image quality of the obtained picture image is degraded.
The CCD shown in FIG. 3 is one such as disclosed in Japanese Patent Application Laid-Open No. 56789/1980. Designated at 2 are anti-blooming gates, denoted at 3 are anti-blooming drains and denoted at 4' are barriers. Between the two anti-blooming parts (gates 2 and drains 3), there are formed first, second and third portions 1R, 1B and 1G divided by the barriers 4'. Such structure is periodically repeated in the horizontal direction. The size (width W) of each of the first, second and third portions 1R, 1B and 1G is the same and an R(red) filter, B(blue) filter and G(green) filter are respectively provided for the first, second and third portions.
In this arrangement, good color picture images are obtainable with the use of the R-G-B stripe filter. However, this arrangement is still disadvantageous in the following points. That is, a complicated signal processing circuit is required to obtain the high range component of the luminance (Y) signal by synthesizing the output from the solid image pickup element. As disclosed in the above-cited Japanese Patent Application, in order to synthesize the high range component of the luminance signal, there are required:
(1) means for separating the output corresponding to each color filter and for sampling the separated the output;
(2) means for amplifying the separated output to a required signal level; and
(3) means for imparting to respective color signals the necessitated phase deviation and for sampling them again.
As the result, the signal processing circuit becomes complex. Further, in this arrangement, the sampling positions are not equidistant, and therefore the resolution is degraded since the resolution is determined by the greatest distance between the sampling positions. On the other hand, when the solid image pickup element shown in FIG. 1 is used in combination with the R-G-B stripe filter and if the device is so set that, with respect to a white (non-colored) object, the output signals from picture element are read out equally and at equal intervals, the high range component of the luminance signal is obtainable only by supplying the signal from the image pickup element to a high pass filter as is discussed in "TV Academic Circle Journal" vol. 33 No. 7 pages 516-522. In such a system, the signal processing circuit becomes simple, but the overall sensitivity of the camera is restricted due to the B(blue) output signal to which the sensitivity of the solid image pickup element is relatively low. Thus, it becomes difficult to ensure high sensitivity of the camera. Although, by changing the combination of the colors of the filter, e.g. to R(red)-Cy(cyan)-G(green), the sensitivity may be improved to some degree, such color signals which enter from the high range component of the luminance distribution into B(blue) signals will be increased in this case. Therefore, the sensitivity to blue of the element is desired as high as possible.